Mitotic karyotypes of species and hybrids of the genus Lemur bred and maintained in the Duke University Primate Facility are established by chromosome banding using the light (LM) and electron microscopes (EM). Meiosis is analyzed by synaptonemal complex (SC) karyotyping of surface spread whole mounts of pachytene spermatocytes with the EM, and by correlated analysis of chiasma figures at diakinesis and metaphase with LM. From banding studies it is concluded that Robertsonian fusion of acrocentric chromosomes represents the predominant mode of karyotypic change in Lemur evolution; centric fission is an unlikely occurrence. A hypothetical ancestral karyotype consisting of acrocentrics is proposed and will be tested and refined. The primary karyotypic differences found between lemur species are in the combinations of acrocentrics forming Robertsonian metacentrics. Several interspecific hybrids that contain as many as eight metacentric/acrocentric pairs are viable and fertile, while one hybrid containing metacentrics with only monobrachial homology may be sterile. Project objectives are predicated on extensions of these findings: (1) The further development and application of LM and EM techniques to provide more comprehensive characterizations of mitotic and meiotic chromosomes and their behavior; (2) elucidation of the way in which Robertsonian rearrangements occur, their effects on fertility, and their significance to evolutionary processes in lemurs; and (3) utilization of details of chromosome structure to reconstruct probable lines of phyletic divergence of the lemurs in particular, and primates in general. Among specific studies projected are evolution of the lemur sex chromosome pair as seen with the EM, and continued breeding experiments to produce specific karyotypes and to test inter- and intra-specific fertility.